Abstract
Laser transformation hardening is effective technique used for selective hardening of components such as turbine blade, camshafts and gears. Laser hardening provides benefits over other selective hardening processes in terms of thermal distortion, control of process and appearance of component. The fiber laser is relatively recent development. The single/low mode fiber lasers have good beam quality, high wall plug efficiency, fiber delivery and powers up to few hundred watts. The beam quality of single mode fiber lasers enable it to be focused to a spot size of few tens of mm which can yield hardened tracks of 100 to 500 mm. These fiber lasers can be extremely useful in localized micro-scale surface hardening to create hardened patterns for improving the wear resistance. This paper is focused on developing analytical thermal model of moving heat sources and integrating it with kinetic hardening model to capture the metallurgical changes induced by fiber lasers. An ideal surface hardening technique should give widest hardened track at minimum case depth. To address this issue, an optimization methodology based on statistical approximation of the physics-based engineering models has been developed.
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Abbreviations
- K:
-
Thermal conductivity (W/mm·K)
- ρ :
-
Density (kg/mm3)
- C:
-
Specific heat capacity (J/kg·K)
- a:
-
Diffusivity (mm2/s)
- I(x, y):
-
Heat intensity (W/mm2)
- T:
-
Temperature (C)
- T0 :
-
Ambient temperature (C)
- t:
-
time (s)
- P:
-
Laser power (W)
- A:
-
Area under heat source (mm2)
- σ :
-
Beam radius (mm)
- AC1 :
-
Eutectoid temperature (C)
- AC3 :
-
Austenization temperature (C)
- Q:
-
Activation energy for transformation (kJ/mol)
- R:
-
Gas constant (J/mol·K)
- τ :
-
Thermal time constant (s)
- Tp:
-
Peak temperature (C)
- D:
-
Diffusion coefficient (mm2/s)
- D0 :
-
Pre-exponential coefficient of C diffusion in ferrite (mm2/s)
- Ce :
-
Austenite C percentage (0.8%)
- Cc :
-
Ferrite C percentage (0.05%)
- fm :
-
Maximum volume fraction of martensite permitted
- fi :
-
Volume fraction of pearlite (C/0.8)
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Gupta, N., Ahirrao, S.B., Paul, S. et al. Modeling of micro-scale fiber laser hardening process and optimization via statistical approximation of the engineering models. Int. J. Precis. Eng. Manuf. 16, 2281–2287 (2015). https://doi.org/10.1007/s12541-015-0293-9
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DOI: https://doi.org/10.1007/s12541-015-0293-9